In 2016, the U.S. Geological Survey (USGS), in cooperation with the San Antonio Water System, began a study to refine previously derived estimates of groundwater outflows from Medina and Diversion Lakes in south-central Texas near San Antonio.
The Edwards aquifer is one of the most permeable and productive carbonate-rock (limestone and dolostone) aquifers in the United States and is the major source of public water supply for more than 1.85 million people in Bexar County. Most recharge to the Edwards aquifer occurs as seepage from streams as they cross the outcrop (recharge zone) of the aquifer. Groundwater outflows from the Medina and Diversion Lake (hereafter referred to as the Medina/Diversion Lake system) have also long been recognized as a potentially important additional source of recharge. A better understanding of the interaction between the Medina/Diversion Lake system and the Edwards aquifer, as well as estimating the recharge to the Edwards aquifer from these lakes, would aid water resource decision makers in better managing the systems.
The objective of this study is to develop a better understanding of the estimated groundwater recharge and quantify the associated uncertainty for the Medina/Diversion Lake system to the Edwards aquifer. The scope of the study is the Medina/Diversion Lake system, which includes Medina Lake and Diversion Lake, as well as the catchment area upstream of the USGS gaging station Medina River near Rio Medina, TX (08180500).
Phase 1: Data Analysis
Earlier estimates of groundwater recharge were based on an ordinary least squares regression analysis. In Phase 1 of the study, three different regression methods were tested in an effort to identify a regression equation that more accurately models the relation between groundwater recharge from the Medina/Diversion Lake system and Medina Lake stage. These included:
(1) a linear-linear ordinary least-squares (OLS) regression equation,
(2) a linear-linear weighted least-squares (WLS) regression equation, and
(3) a log-log weighted least-squares (log-log WLS) regression equation.
Results of these analysis are published as Appendix 1 to SIR 2004-5209, A water-budget analysis of Medina and Diversion Lakes and the Medina/Diversion Lake system, with estimated recharge to Edwards aquifer, San Antonio area, Texas. The results are also summarized in FS 2017-3008, Refining Previous Estimates of Groundwater Outflows from the Medina/Diversion Lake System, San Antonio Area, Texas.
Phase 2: Data Collection
Preliminary findings of Phase 1 of the study have identified periods where the relation between Medina Lake stage and groundwater recharge estimates are not well defined. Additional hydrologic data are needed to address data gaps and to validate the statistical relation developed as part of Phase 1.
To accomplish this, hydrologic data will be collected to complete the overall water-budget for the Medina/Diversion Lake system. The water-budget equation incorporates measurable components of inflow and outflow to solve for unknown gains or losses from the lake system. The measurable components include: surface water inflow and outflow, precipitation, evaporation, and change in storage. The unknown gains and losses are represented by the residual of all the measurable components—or water that is not accounted for. The overall water-budget equation for the Medina/ Diversion Lake system can be written as follows:
GWout = P – E + SWin – SWout – ΔS,
Where:
GWout is groundwater outflow (loss from the lake system, assumed to recharge the groundwater system);
P is precipitation on the lake;
E is evaporation from the lake surface;
SWin is surface-water inflow to the lake;
SWout is surface-water outflow from the lake; and
ΔS is change in lake storage.
- Precipitation on the lake (P) and evaporation from the lake (E) will be measured at USGS gaging station Medina Lake Meteorological Station near Rio Medina, TX (293355098560601)
- Surface-water inflow (SWin) to the lake will be measured at two USGS gaging stations: Medina River above English Crossing near Pipe Creek, TX (08178980) and Red Bluff Creek at FM 1283 near Pipe Creek, TX (08179110)
- Surface-water outflows (SWout) from the lake will be measured at USGS gaging station Medina River near Rio Medina, TX (08180500)
- change in lake storage (ΔS) will be measured using a stage-storage rating for the USGS gaging stations Medina Lake near San Antonio, TX (08179500) and Diversion Lake near Rio Medina, TX (08180010)
Below are publications associated with this project.
Refining previous estimates of groundwater outflows from the Medina/Diversion Lake system, San Antonio area, Texas
Hydrogeology, hydrologic budget, and water chemistry of the Medina Lake area, Texas
Geologic framework and hydrogeologic characteristics of the outcrops of the Edwards and Trinity aquifers, Medina Lake area, Texas
A water-budget analysis of Medina and Diversion Lakes and the Medina/Diversion Lake system, with estimated recharge to Edwards aquifer, San Antonio area, Texas
Below are partners associated with this project.
- Overview
In 2016, the U.S. Geological Survey (USGS), in cooperation with the San Antonio Water System, began a study to refine previously derived estimates of groundwater outflows from Medina and Diversion Lakes in south-central Texas near San Antonio.
The Edwards aquifer is one of the most permeable and productive carbonate-rock (limestone and dolostone) aquifers in the United States and is the major source of public water supply for more than 1.85 million people in Bexar County. Most recharge to the Edwards aquifer occurs as seepage from streams as they cross the outcrop (recharge zone) of the aquifer. Groundwater outflows from the Medina and Diversion Lake (hereafter referred to as the Medina/Diversion Lake system) have also long been recognized as a potentially important additional source of recharge. A better understanding of the interaction between the Medina/Diversion Lake system and the Edwards aquifer, as well as estimating the recharge to the Edwards aquifer from these lakes, would aid water resource decision makers in better managing the systems.
The objective of this study is to develop a better understanding of the estimated groundwater recharge and quantify the associated uncertainty for the Medina/Diversion Lake system to the Edwards aquifer. The scope of the study is the Medina/Diversion Lake system, which includes Medina Lake and Diversion Lake, as well as the catchment area upstream of the USGS gaging station Medina River near Rio Medina, TX (08180500).
Phase 1: Data Analysis
Earlier estimates of groundwater recharge were based on an ordinary least squares regression analysis. In Phase 1 of the study, three different regression methods were tested in an effort to identify a regression equation that more accurately models the relation between groundwater recharge from the Medina/Diversion Lake system and Medina Lake stage. These included:
(1) a linear-linear ordinary least-squares (OLS) regression equation,
(2) a linear-linear weighted least-squares (WLS) regression equation, and
(3) a log-log weighted least-squares (log-log WLS) regression equation.Results of these analysis are published as Appendix 1 to SIR 2004-5209, A water-budget analysis of Medina and Diversion Lakes and the Medina/Diversion Lake system, with estimated recharge to Edwards aquifer, San Antonio area, Texas. The results are also summarized in FS 2017-3008, Refining Previous Estimates of Groundwater Outflows from the Medina/Diversion Lake System, San Antonio Area, Texas.
Phase 2: Data Collection
Preliminary findings of Phase 1 of the study have identified periods where the relation between Medina Lake stage and groundwater recharge estimates are not well defined. Additional hydrologic data are needed to address data gaps and to validate the statistical relation developed as part of Phase 1.
To accomplish this, hydrologic data will be collected to complete the overall water-budget for the Medina/Diversion Lake system. The water-budget equation incorporates measurable components of inflow and outflow to solve for unknown gains or losses from the lake system. The measurable components include: surface water inflow and outflow, precipitation, evaporation, and change in storage. The unknown gains and losses are represented by the residual of all the measurable components—or water that is not accounted for. The overall water-budget equation for the Medina/ Diversion Lake system can be written as follows:
GWout = P – E + SWin – SWout – ΔS,
Where:
GWout is groundwater outflow (loss from the lake system, assumed to recharge the groundwater system);
P is precipitation on the lake;
E is evaporation from the lake surface;
SWin is surface-water inflow to the lake;
SWout is surface-water outflow from the lake; and
ΔS is change in lake storage.- Precipitation on the lake (P) and evaporation from the lake (E) will be measured at USGS gaging station Medina Lake Meteorological Station near Rio Medina, TX (293355098560601)
- Surface-water inflow (SWin) to the lake will be measured at two USGS gaging stations: Medina River above English Crossing near Pipe Creek, TX (08178980) and Red Bluff Creek at FM 1283 near Pipe Creek, TX (08179110)
- Surface-water outflows (SWout) from the lake will be measured at USGS gaging station Medina River near Rio Medina, TX (08180500)
- change in lake storage (ΔS) will be measured using a stage-storage rating for the USGS gaging stations Medina Lake near San Antonio, TX (08179500) and Diversion Lake near Rio Medina, TX (08180010)
- Publications
Below are publications associated with this project.
Refining previous estimates of groundwater outflows from the Medina/Diversion Lake system, San Antonio area, Texas
IntroductionIn 2016, the U.S. Geological Survey (USGS), in cooperation with the San Antonio Water System, began a study to refine previously derived estimates of groundwater outflows from Medina and Diversion Lakes in south-central Texas near San Antonio. When full, Medina and Diversion Lakes (hereinafter referred to as the Medina/Diversion Lake system) (fig. 1) impound approximately 255,000 acre-Hydrogeology, hydrologic budget, and water chemistry of the Medina Lake area, Texas
A three-phase study of the Medina Lake area in Texas was done to assess the hydrogeology and hydrology of Medina and Diversion Lakes combined (the lake system) and to determine what fraction of seepage losses from the lake system might enter the regional ground-water-flow system of the Edwards and (or) Trinity aquifers. Phase 1 consisted of revising the geologic framework for the Medina Lake area.Geologic framework and hydrogeologic characteristics of the outcrops of the Edwards and Trinity aquifers, Medina Lake area, Texas
The hydrogeologic subdivisions of the Edwards aquifer outcrop in the Medina Lake area in Medina and Bandera Counties generally are porous and permeable. The most porous and permeable appear to be hydrogeologic subdivision VI, the Kirschberg evaporite member of the Kainer Formation; and hydrogeologic subdivision III, the leached and collapsed members, undivided, of the Person Formation. The porositA water-budget analysis of Medina and Diversion Lakes and the Medina/Diversion Lake system, with estimated recharge to Edwards aquifer, San Antonio area, Texas
In January 2001, the U.S. Geological Survey—in cooperation with the Edwards Aquifer Authority—began a study to refine and, if possible, extend previously derived (1995–96) relations between the stage in Medina Lake and recharge to the Edwards aquifer to include the effects of reservoir stages below 1,018 feet and greater than 1,046 feet above National Geodetic Vertical Datum of 1929. The principal - Partners
Below are partners associated with this project.